1. Field
The field of the invention is endless track assemblies for snow grooming vehicles, and more particularly the cleat assemblies thereof, including structures for fastening the cleats to the flexible plastic belting of such tracks.
2. State of the Art
Snow groomer vehicles use endless tracks made up of flexible plastic belts made continuous by lacing their ends together. Actual lacing thread may be used, although lacing joint assemblies are more commonly employed, being a combination of metallic hinge plates and an associated hinge pin. The snow grooming vehicle commonly has an endless track assembly on each of its sides, each comprising a number of fabric reinforced plastic belts. The belts are spaced apart to provide a broad base for the track while utilizing minimum amounts of belting. Steel cleat assemblies are bolted across the individual belts at intervals, tieing them together into a track assembly. Each assemblied track is engaged by a power-transmitting sprocket wheel, which forces the belts to travel together around a set of guiding wheels called bogies. The powered belt imparts horizontal shear forces to the cleats, which engage the snow to propel the vehicle. Extensive development has gone into the design of the elongate cleat members, with the objectives of providing maximum forward traction along with substantial resistance to side slipping. Cleat constructions are disclosed in U.S. Pat. Nos. 3,765,731, 4,560,211, 4,281,882 and 4,059,315. Typically, the ground contacting cleat, also called a "grouser", is fastened to the outside of the flexible belting by bolts and nut assemblies installed in matching holes in the grouser, the belt, and a metal backing plate on the inside of the belt. A large number of bolt and nut assemblies are required to spread the high shearing forces among the belt holes. The horizontal force on the ground engaging part of the cleat also results in light moment loads which must be resisted by the stems of the bolts. Failure of the bolts in bending is a too frequent common occurrence, and is largely caused by the moment force applied to the portion of the stem at the junction of the threads and the unthreaded shank, resulting in stress concentration. U.S. Pat. No. 5,201,574 discloses an assembly with an improved cleat retaining bolt and nut assembly configured to position the threaded portion of the bolt away from the bending resistant portion of the stem. However, the bending moment upon the bolt remains excessive and fatigue limits continue to be exceeded resulting in continued failures.
An improved cleat assembly design is needed, which in particular reduces the stress level of the bolts to below their fatigue limits.